Applying vitreous enamel



Dec. 15, 1970 J- T. GARTRELL 3,546,909

I APPLYING VITREOUS ENAMEL Filed April 9, 1968 2 Sheets-Sheet z INVENTORfom 7? aarfreil ATTORNEYS United States Patent O US. Cl. 72-46 7 ClaimsABSTRACT OF THE DISCLOSURE The invention relates to a process andapparatus for applying vitreous enamel by preheating metal sheet whilewound in a coil, uncoiling the preheated sheet and progressing itforward while preferably stabilizing the temperature so that the sheetis at vitreous enameling temperature, applying dry powder vitreousenamel frit or slip to one or both sides of the heated sheet, meltingthe frit in contact with the sheet to form a molten vitreous enamelcoating on the sheet and cooling the sheet and coating. The sheet isthen in the preferred embodiment cooled to a temperature at which theenamel remains plastic and then deformed while the sheet and enamel areat that temperature. The temperature for deforming is desirably attainedby cooling and then reheating slightly.

CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part ofmy co-pending application Serial No. 565,997 filed July 18, 1966, andnow US. Pat. No. 3,412,589, for Process for Porcelain Enameling andForming Sheet Metal.

DESCRIPTION OF INVENTION The present invention relates to a process andapparatus for applying vitreous enamel to metal sheet, such as steel,stainless steel, aluminum, or other suitable metal sheet.

When reference is made herein to sheet, it will be evident that therelatively light gauge metal is capable of being handled in a coil, andit may be designated a sheet, a strip, or otherwise. The gauge may be asthick a 16 gauge or slightly thicker.

A purpose of the invention is to expedite the application of vitreousenamel to metal sheet by preheating the metal sheet and applying drypowder frit or slip to the metal sheet when it is heated to atemperature at which the enamel will fuse.

A further purpose is to preheat the sheet as a coil, to unwind andforwardly progress the sheet from the coil, and to apply the dry powderfrit directly to one or both sides of the sheet heated to enamelingtemperature.

A further purpose is to regulate the temperature of the sheet prior toapplying the frit, desirably by adding an increment of heat.

A further purpose is to apply the dry powder frit to the sheet either byelectrostatic, mechanical, airblowing or other means.

A further purpose is to cool the sheet and the enamel after applying thepowder frit, desirably by an air stream or air blanket at reducedtemperature.

A further purpose is to take off the enameled sheet from the enamelingmechanism, at a temperature at which the enamel remains plastic, and todeform the sheet and enamel while it is at that temperature.

A further purpose is after enameling and cooling the sheet to slightlyheat it to regulate its temperature to a temperature at which the enamelis plastic and deform the sheet and enamel while at that temperature.

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Further purposes appear in the specification and in the claims.

In the drawing 1 have chosen to illustrate a few only of the numerousembodiments in which the invention may appear, selecting the forms shownfrom the standpoints of convenience in illustration, satisfactoryoperation and clear demonstration of the principles involved.

FIG. 1 is a diagrammatic plan view of an enameling and corrugatingmechanism according to the invention.

FIG. 1a is a view similar to FIG. 1 showing a varia tion in thecorrugating mechanism.

FIG. 2 is a diagrammatic fragmentary end elevation of the corrugatingmechanism at an early stage, showing a single upper corrugating roll anda pair of lower corrugating rolls.

FIG. 3 is a diagrammatic fragmentary end elevation at a more advancedpoint along the corrugating mechanism showing additional corrugatingrolls in the upper and lower groups.

FIG. 4 is a side elevation of a modified form of corrugating rolls foruse in the invention.

Describing in illustration but not in limitation and referring to thedrawings:

An extensive industry has developed relating to the production ofvitreous enameled metal sheet, applied for example on plain carbonsteel, stainless steel, aluminum, or other metal base. The metal basemay be an alloy composition especially intended for vitreous enamelingas Well known in the art.

The operation of vitreous enameling especially when applied onrelatively large areas, has in the past been quite slow. This has beendue to two factors. One reason for the slowness of the prior artvitreous enameling is that they have depended on taking a sheet or stripand heating it as it is progressed longitudinally. Heating under theseconditions using desirable rates of heat input is necessarily a slowoperation.

A further purpose for the slowness of the prior art enameling is thatthey have relied upon bringing the powder frit or slip, which is reallya powder glass, into a coatable form by adding a liquid medium such aswater, and in the actual enameling this must be eliminated withcorresponding delay in the operation. Calton U.S. Pat. 2,428,307,granted Sept. 30, 1947 for Method of an Apparatus for PorcelainEnameling Sheet Metal.

By the present invention the metallic sheet in coil form is preheated toa temperature at least as great as 1000 F. in the case of steel sheet,and preferably just below the temperature of fusion of the frit, thenthe preheated coil is uncoiled and advanced while its temperature isregulated to the correct temperature for fusion of the frit, and thenthe dry powder frit is applied to one or both sides of the sheet whileit is at the elevated temperature so that the frit will fuse on themetal surface as vitreous enameled coating.

The closer the temperature of preheating can be regulated to thetemperature for fusing the frit, the less heat will have to be added asthe sheet is progressing to the point of enameling and therefore thefaster the overall operation.

If the sheet is desired in flat form, it is not necessary to corrugateor otherwise deform it. The invention, however, lends itself tocorrugating or otherwise deforming the sheet after enameling. For thispurpose the temperature of the sheet and the enamel is lowered to atemperature at which the enamel is soft or plastic but is not molten,for example a temperature of 1150 to 1250 F., or approximately 200 to300 F. below the fusion temperature of a commercial porcelain enamel,which is around 1450 F. The achieving of this plastic temperature isbest done by cooling the enamel and the sheet after enameling as by anair blanket, and then adding a slight amount of additional heat in orderto properly regulate the temperature to the enamel plastic temperature.The sheet can then be corrugated or otherwise deformed, for example deepdrawn, at the plastic temperature of the enamel without cracking theenamel. Finally the sheet is cut to suitable size, as by a flying hear,either before or after the metal working operation.

As shown in FIG. 1, coils of sheet 21 are mounted on reels in a mannerwhich will permit unrolling of the sheet, the reels being supported oncars or dolleys 22 running on a railway track 23. The cars are run inthe direction of the arrow 24 into a tunnel furnace 25 whose roof hasbeen omitted in FIG. 1 to permit better illustration. The tunnel furnacehas suitable incremental heating chambers 26 and 27 separated byswinging doors 28, it being understood that as many different incrementsor chambers will be used as desired. The fully heated or fully preheatedcoil 20 is positioned in a final chamber 30 in which the sheet isuncoiled and threaded through suitably driven pinch rolls 31 and thenfed through a temperature adjusting or final heating furnace 32 suitablyheated as by electric resistors 33. The intention is to add only a minorincrement of heating to adjust to the actual enameling temperature infurnace 32.

From the furnace 32 the sheet passes continuously through enamel spraybooth 34, suitably as a long stretch of sheet free from guiding rollers,and there it has deposited thereon, preferably on both sides, dry powderfrit or slip, desirably from an electrostatic spraying mechanism 35 aswell known in the art. While electrostatic spraying is preferred, itwill be understood that the dry powder frit can be applied bymechanically propelling it or propelling it in a stream of air or by anyother well recognized means of spraying dry powder.

The spray booth 34 is provided with a suitable stack 36 to eliminatedust.

As soon as the dry frit or slip contacts the metallic sheet heated to atemperature which will fuse the enamel, it adheres to the sheet andfuses thereon, making a layer of enamel on one or both sides of thesheet as desired.

Beyond the spray booth 34 and suitably separated therefrom, is a coolingchamber 37 which has on the top and bottom opposite the sheet downwardlyand upwardly directed ports 38 through whichva cool air blanket orstream is applied, sufficient to cool the enamel and the sheet to atemperature at which the enamel is no longer molten. Then the sheetcontinues through a heat control furnace or tunnel 40 suitably heated byelectric heating elements 41 and capable of adjusting the temperature ofthe enamel and the sheet by adding a relatively slight amount of heat tomake the enamel plastic but not molten.

Then the sheet with a plastic enameled layer thereon is subjected todeformation, for example, to corrugation. In FIG. 1 the sheet passesthrough a corrugator 42, as well known in the art, bringing the sheetinto contact with progressive top and bottom corrugating rolls. Thus asshown in FIG. 2, the sheet may first be contacted near the middle in thelongitudinal direction by an upper corrugating roll 43 and lower spacedcooperating corrugating rolls 44 and 45.

At a more forward position as shown in FIG. 3 the sheet may be contactedwith a set of spaced upper corrugating rollers 46, 47 and 48 cooperatingwith lower corrugating rolls 50 and 51, and so on progressively untilthe corrugation is complete.

Then the sheet is severed transversely by a flying shear 52, after whichthe severed sheets are taken off by a transfer mechanism not shown.

Other techniques for corrugating may be used as desired.

In FIG. 10, after leaving the heat control furnace 40, the sheet may besevered by a flying shear 52 and then received on a transfer table 53 tobe transferred by a transfer mechanism 54 and then to pass through acorrugator 55 having top and bottom cooperating corrugating rolls 56 and57 as shown in FIG. 4. Finally the corrugated sheet is discharged at 58.

It will be evident that in the operation according to the invention mostof the time taken up formerly in heating the steel for preheat will besaved by preheating the steel as a coil, and also the time taken todrive off moisture will be saved since the frit is being applied as adry powder. Thus speeds of the order of feet per minute or more foradvancement of the sheet can be obtained.

It will also be evident that various colors of enamel may be produced,for example by providing alternatively used spray booths for differentcolors in the production system.

In view of my invention and disclosure, variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art to obtain all or part of the benefits of myinvention without copying the process and apparatus shown, and I,therefore, claim all such insofar as they fall within the reasonablespirit and scope of my claims.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A process of applying vitreous enamel to metal sheet, which comprisespreheating the metal sheet wound in a coil, uncoiling the preheatedmetal sheet and progressing it forward, regulating the temperature ofthe sheet as it is progressed forward to vitreous enameling temperatureprior to applying a dry powder vitreous enamel frit, applying dry powdervitreous enamel frit to at least one side of the heated sheet, meltingthe frit in contact with the sheet to form a molten vitreous enamelcoating on the sheet, and cooling the sheet and coating.

2. A process of claim 1, which comprises electrostatically applying thedry powder frit to the sheet.

3. A process of claim 1, which comprises blowing the dry powder fritagainst the sheet by heated air to apply the frit.

4. A process of claim 1, which comprises applying the frit to both sidesof the sheet.

5. A process of claim 1, which comprises cooling the sheet and frit by astream of relatively cool air.

'6. A process of claim 1, which comprises cooling the sheet and coatingto a temperature at which the enamel remains plastic and deforming thesheet and enamel while at that temperature.

7. A process of claim 1, which comprises after cooling further heatingthe sheet and enamel to a temperature at which the enamel is plastic,and deforming the sheet and enamel while at that temperature.

References Cited UNITED STATES PATENTS 2,480,711 8/1949 Calton 1l7--1293,058,443 10/1962 Paton 11723 3,167,442 1/1965 Brooks 1171O 3,426,7302/1969 Lawson et al. l1717 3,163,553 12/1964 Commonday et al. 117-22WILLIAM D. MARTIN, Primary Examiner R. M. SPEER, Assistant Examiner US.Cl. X.R. 1l710, 17, 23

